Taxicab advertising sign



FIG. 1 is a front and top perspective view of an ornamental design for a taxicab advertising sign showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a front end elevational view thereof, and

FIG. 5 is a side elevational view thereof. 

The ornamental design for a taxicab advertising sign, substantially as shown and described. 